1. Field of the Invention
The present invention relates to a liquid container and a package thereof. More specifically, the present invention relates to: a liquid container suitable for storing liquid such as ink used in inkjet printing; and a package thereof. In addition to a general printing apparatus, the liquid container of the present invention is also applicable to apparatuses such as: a copying machine; a facsimile having a communication system; and a word processor having a printing unit. Furthermore, the liquid container is also applicable to a liquid supply source of an industrial printing apparatus combined in a complex manner with various kinds of processing apparatuses.
2. Description of the Related Art
In an inkjet printing apparatus, a printing head and a liquid container (hereinafter, also referred to as an ink tank) are used in general. The ink tank is connected to the printing head, and thereby supplies liquid such as printing ink to the printing head. When printing is carried out, ink is ejected in accordance with image data through a fine ejection opening provided to the printing head, and thereby is landed on a printing medium. In this way, a desired image is formed.
Ink is supplied to the printing head from the ink tank as an ink supply source. As a method of supplying ink to a printing head, there is a method in which an ink tank containing ink is mounted on a carriage, and directly supplies the ink to the printing head. Additionally, there is another method in which an ink tank is arranged to a fixed portion of an apparatus, and with which ink is communicated between the ink tank and a printing head by using a supply tube. Here, in both methods, an ink tank is generally detachably attached to a printing apparatus so that the ink tank can be replaced with a new one when there is substantially no remaining amount of ink stored in the ink tank.
In recent years, the inkjet printing technology has come to be applied in a wide range of fields. The application of the inkjet printing technology has expanded into industrial uses, in addition to personal or home uses and office uses. Hence, inkjet printing apparatuses suitable for various uses have been developed. Additionally, as ink used therein, adopted are kinds of ink exhibiting characteristics favorable to various uses.
Kinds of ink are broadly categorized into: ink mainly containing dye component as a coloring material (hereinafter, referred to as dye ink); and ink mainly containing pigment component as a coloring material (hereinafter, referred to as pigment ink). In a case of use requiring light resistance and gas resistance of a printed subject, for example, use for a production of an outdoor display media, the pigment ink is often used particularly so that the sufficient fastness of an image can be secured.
However, in comparison with the dye ink, the pigment ink has various problems in terms of handling. For example, dispersibility of pigment component of a coloring material in the ink is one of the problems.
For example, pigment component does not dissolve into an ink solution like dye component, and floats in a dispersed state. For this reason, pigment particles gradually settle out due to the action of gravity, if an ink tank is left to stand still for a certain period of time. This causes a variation in the concentration distribution of the pigment particles in a vertical direction. In other words, a layer having a high concentration of the coloring material is formed in a lower part of the ink tank, and a layer having a low concentration of the coloring material is formed in an upper part of the ink tank. When printing is started and continued with this state being maintained, outputted images have a density variation between parts recoded in an earlier stage and in a later stage in using the ink tank.
For example, consider a configuration where an ink supply port is arranged in a part which is a bottom of an ink tank at a time when mounted, and where thus the ink tank supplied ink to a printing head. In this case, if printing is started with the ink tank being mounted in a state having the variation in concentration distribution, the ink is supplied initially from a lower layer having the higher concentration of the coloring material. As a result, an image is outputted which has a higher density than a required one. Afterward, the density of the image gradually becomes lower as the printing is continued and the ink in the ink tank is further consumed. At about the time when only a small amount of the ink remains, the remaining ink is only the one having the lower concentration of the color material than the ink at the start of the printing. Then, a printed subject may possibly have an insufficient density that cannot be expressed properly even if the printed subject is printed in accordance with the same image data as that used at the start of the printing. Particularly, the large diameter or the large specific gravity of pigment particle results in a remarkably large settling tendency. This produces such a large variation in concentration distribution that the influence on an image appears, even when the ink tank has been left out of use only for a few days.
Additionally, as for the dye ink, content component sometimes becomes separate from each other in the course of freezing in a case where the ink freezes in a cold climate area or the like. In this case, it leads to uneven distribution of the dye component itself in the ink tank, and a concentration gradient sometimes occurs in the dye ink although the gradient is not as severe as that in the case of the pigment ink.
As has been described above, the variation in concentration of a coloring material of ejected ink causes not only a problem of generating a density variation between output images in an earlier stage and a later stage in using an ink tank; but also the collapse of a color balance in a color inkjet printing system which expresses a desired hue under a predetermined color balance by using a plurality of color inks. Accordingly, this produces a problem that the unevenness in an image causes the image deterioration to be recognized.
Each of ink tanks disclosed respectively in Japanese Patent Laid-Open No. 2001-270131 and No. 2001-293880 is provided with a tubular member extending from an ink supply port of the tank into the interior of the tank. An ink absorber is included in the interior of the ink tank, and the tubular member is surrounded by this absorber. A plurality of holes used for allowing ink to flow into the tubular member are provided in a side face of the tubular member. The ink flows into the interior of the tubular member through the plurality of holes provided in the side face thereof. To be more precise, the ink flows into the interior of the tubular member not only from the holes close to the position of the supply port but also from the holes located far from the position of the supply port. Then, the ink is delivered to the outside of the tank from the supply port. In this manner, influence of a concentration gradient of ink coloring material is reduced, whereby the concentration of the coloring material of the delivered ink is maintained within a desired range.
However, in each of the above conventional examples, the ink absorber is provided in the interior of the ink tank, and the ink is contained in this absorber. In a case of an ink tank which does not include an ink absorber in order to increase the containing amount of ink, and which thus directly contains ink, no means that prevents coloring material component from settling out is provided. Consequently, the variation in concentration distribution of color material in the ink tank is larger than in the above conventional examples.
A period during which coloring material component settles as an ink tank is left to stand still is not only a period during which the ink is out of use after having been mounted in a printing apparatus (hereinafter, refer to an out-of-use period). The tank is left to stand still also in a period after the tank is manufactured until a user starts to use the tank (hereinafter, referred to as an unused period), that is, the period including: a distribution period; a display period for sale; and furthermore, a period during which a user or the like stores the tank. In reality, the unused period is longer than the out-of-use period, and it is considered that the variation in concentration distribution of color material becomes large in the unused period.
After the ink tank is mounted in the printing apparatus, the printing apparatus can perform an appropriate stirring operation for the ink tank. For example, the stirring operation is carried out by pressurizing and decompressing an ink supply path, such as a tube connected to the tank; and thus by causing the ink to flow or move inside the tank. In this manner, a stirring effect acts upon an entirety of the ink contained in the tank, and this achieves a state where the variation in concentration distribution is small (a state of the uniform distribution of a coloring material).
However, such an active stirring operation cannot be performed during the unused period. As a result, settling of a coloring material or pigment component progresses, and the variation in concentration distribution in a vertical direction of the tank may become extremely large in some cases. In a state where such large variation in concentration distribution have been generated, that is, a state where the coloring material is concentrated near an ink supply port, it becomes more difficult to reduce the variation in concentration distribution. A stirring effect cannot be sufficiently obtained in some cases at an early stage after the tank is mounted, even if the ink stirring operation inside the tank is performed by pressurizing and decompressing the ink supply path, such as the tube, connected to the tank. In particular, at an early stage after the tank starts to be used, it is inevitable to use highly concentrated ink resulting from the settling of a coloring material near the ink supply port of the tank. For this reason, an image having an extremely high density may be formed.
Consequently, in general, a user is recommended to perform a stirring operation, which is called “shaking by hands,” prior to mounting of the tank to the apparatus. Specifically, that is an operation in which the user himself or herself shakes the ink tank, and thus moves the whole of the tank. When a user mounts a tank on an apparatus, and starts to use it without performing such a stirring operation because of his or her forgetting or neglect, an image having a high density may sometimes be formed in an early stage of printing. It is desirable to perform a stirring operation on the tank first, thereby improving the concentration distribution of color material, and then to perform printing. However, such an operation has to be manually performed by the user, while it is desirable that the operation be less troublesome. This situation brings about a conflicting problem therebetween.